Field of the Invention
The present invention relates to a honeycomb structure. More particularly, it relates to a honeycomb structure which is a catalyst carrier and also functions as a heater when a voltage is applied thereto and which can inhibit an unevenness of a temperature distribution when the voltage is applied thereto and can enhance heat shock resisting properties.
Background Art
Heretofore, a product in which a catalyst is loaded onto a honeycomb structure made of cordierite has been used for a treatment of harmful substances in an exhaust gas discharged from a car engine. Furthermore, it has also been known that a honeycomb structure formed from a sintered silicon carbide body is used for purification of the exhaust gas (e.g., see Patent Document 1).
When the exhaust gas is treated by the catalyst loaded onto the honeycomb structure, it is necessary to raise a temperature of the catalyst to a predetermined temperature, but the catalyst temperature is low at start of the engine, which has caused a problem that the exhaust gas is not sufficiently purified.
Consequently, there has been investigated a method of disposing a heater made of a metal on an upstream side of the honeycomb structure onto which the catalyst is loaded to raise the temperature of the exhaust gas (e.g., see Patent Document 2). Furthermore, a method has been investigated in which the catalyst is loaded and used on the heater made of the metal (e.g., see Patent Document 3).
Furthermore, it has been suggested that a honeycomb structure body made of a ceramic material is used as “a heatable catalyst carrier” (e.g., see Patent Document 4).    [Patent Document 1] JP 4136319    [Patent Document 2] JP 2931362    [Patent Document 3] JP-A-5-144549    [Patent Document 4] WO 2011/125815